757 - I have a pretty similar issue. The best thing I have been told (as my ECG always produces a spurious reading) is to take your Gatwick exercise ECG printout with you whenever you undertake a test. A quick reference to that ream of paper by the AME should suffice (although I have little idea how to interperet it).
Ben - Have you undertaken an exercise ECG with your authority medical staff following your Echo/X-ray? If you have (as it was the next step in my case) that should be sufficient to satisfy the authority's cardiologist (assuming it is a pass that is) and allow issuance of your medical.